Although hyperhomocysteinemia is an independent risk factor for myocardial infarction and stroke, the mechanistic link between homocysteine (Hcy) and arteriosclerosis is unknown. We have proposed hypomethylation as a specific mechanism by which Hcy inhibits endothelial regeneration that leads to cardiovascular disease [11. Our plan in the ongoing research "Inhibition of Endothelial Growth by Homocysteine" (ROl-I-IL67033) is to elucidate the molecular mechanisms by which Hcy inhibits endothelial cell (EC) growth and to evaluate its role in a hyperhomocysteinemic mouse model. EC growth is a key step of vasculogenesis and angiogenesis. The growth inhibitory effect of Hcy on EC growth suggests a role in the development of atherosclerosis and vasculogenesis. The basic hypothesis of this proposed project is that Hcy inhibits EC differentiation and vascular development. This is based on our previous finding that Hcy selectively inhibits EC growth, and our new observation that there is a decrease in vascularization in hyperhomocysteinemic mice. This hypothesis is supported by studies from others showing that Hcy inhibits angiogenesis in vitro and in vivo. We plan to investigate the effect of Hcy on EC differentiation and vasculogenesis using human embryonic stem (ES) cells, and to test the role of the targeting molecules during this process. In Aim 1, we will determine the effect of Hcy on EC differentiation by embryoid body (EB) formation using human ES cell line 1-19 clone (NIH Code: WA09) from WiCell Research Inst (Madison, WI), which has been validated for EC differentiation. In Aim 2, we will assess the status and the role of Ras demethylation and cyclin A inhibition in Hcy signaling in EC derived from human ES cells. We anticipate that our studies will advance the body of knowledge that will establish a mechanistic connection between Hcy and impaired human vasculogenesis, and will help in achieving our primary goal in the ongoing research, which is to understand the effect of Hcy in human endothelial biology. [unreadable] [unreadable]